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Full text of "The manufacture and properties of iron and steel"

CHAPTER XX.
STEEL CASTINGS,
SECTION XXa.—Definition of a steel casting.—A steel casting must be made of steel cast in a fluid state into the desired shape. It has been the practice of some persons to make castings from pig-iron and steel melted in a cupola, although every metallurgist knows that the metal is altered very much by remelting, and that the changes in silicon, manganese and carbon depend on all the uncertain factors of temperature and exposure. In melting pig-iron, the carbon usually changes very little, for the content of this metalloid was adjusted in the blast furnace to about the absorptive capacity corresponding to the manganese and silicon, and as the conditions in the cupola are similar to those in the blast furnace, it follows that a metal which is the normal product of one will not be fundamentally altered by passing through the other.
But a mixture of steel and iron is not a normal product of any furnace, and in the cupola there is a tendency to make radical changes in the composition by absorption of carbon. Thus, by the unnatural union of pig and scrap, and by uncertain changes in silicon, manganese and carbon, there is produced a hybrid metal which is useful for special purposes, but which is fundamentally different from any kind of steel. It is true that scrap and iron are melted together to make open-hearth steel, but this is done under an oxidizing flame and, either during the melting or afterward, the metalloids are almost entirely eliminated, giving a definite starting point from which a known and regular metal can be made by the addition of recarburizers.
Sometimes castings of cupola metal, made either with or without scrap, are heated in contact with iron oxide in order to burn the contained metalloids. The product is a more or less tough metal, known as malleable iron, which is extensively employed in making email, thin, or complicated shapes that could scarcely be poured in